Ditto. I curse like a drunken sailor sometimes and this would be one of those times! I start out polite; "No, sorry (our dogs can't meet), we're busy training!" Then I'll get a little more curt; "My dog is NOT friendly with other dogs, I don't care how friendly your dog is!" Then I resort to some violence; "My dog WILL BITE your dog!" Then human physical violence; "I WILL CUT YOU!" That's basically how my escalated aggression plays out with twats like in the OP!